[vim/vim] Regresion in patch 9.2.0110: can't select text in terminal with tmux with Shift + Left-Click + Drag (Issue #19580)

Dominique Pelle

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Mar 5, 2026, 12:22:52 PM (yesterday) Mar 5

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DominiquePelle-TomTom created an issue (vim/vim#19580)

Steps to reproduce

Starting from patch 9.2.0110, I can no longer select text
with Shift + Mouse Left-Click + Drag in the terminal with tmux.
When I start selecting, the selection is randomly cancelled
almost as soon as I drag the mouse.

It does not happen with "vim -clean". I minimized my .vimrc
to just one plugin which triggers it:

call plug#begin()
Plug 'DanBradbury/copilot-chat.vim'
call plug#end()

If I keep my original .vimrc (which uses several plugins and
personal settings) but only comment out the line that loads
the 'DanBradbury/copilot-chat.vim' plugin, it works fine.

This is the Vim commit, which introduces the regression:

commit 7ba60f17c22ef81680f25f8c3225b4edb55ddd7c (HEAD -> master, tag: v9.2.0110, upstream/master)
Author: Foxe Chen <chen...@gmail.com>
Date:   Wed Mar 4 20:52:25 2026 +0000

    patch 9.2.0110: No support for terminal synchronization mode

    Problem:  No support for terminal synchronization mode
    Solution: Add DEC 2026 support using the 'termsync' option
              (Foxe Chen).

CC: @64-bitman (author of above commit)

Reproducing the bug requires using:

vim 9.2.0110 (earlier versions were fine)
vim inside tmux (without tmux, it's fine)
the plugin https://github.com/DanBradbury/copilot-chat.vim (without the plugin it's fine)

CC: @64-bitman (author of above commit)

Expected behaviour

I should be able to select text in the terminal with Shift + Left Click + Drag as I used to prior to vim 9.2.0110.

Version of Vim

9.2.0110

Environment

OS: Ubuntu-22.04.5
Terminal: Alacritty-0.16.1 + tmux next-3.7

Logs and stack traces

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Christian Brabandt

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Mar 5, 2026, 1:49:57 PM (yesterday) Mar 5

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chrisbra left a comment (vim/vim#19580)

If you disable termsync, does it work? Or what about setting t_BS and t_ES to an empty string?

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Dominique Pelle

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Mar 5, 2026, 6:53:56 PM (yesterday) Mar 5

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DominiquePelle-TomTom left a comment (vim/vim#19580)

@chrisbra wrote:

If you disable termsync, does it work?

The bug still happens if I add set notermsync in the .vimrc.

Or what about setting t_BS and t_ES to an empty string?

The bug no longer happen if I add set t_BS= t_ES=.

In other words, the bug does not happen with this .vimrc:

set t_BS= t_ES=
call plug#begin()
Plug 'DanBradbury/copilot-chat.vim'
call plug#end()

But the bug happens with:

call plug#begin()
Plug 'DanBradbury/copilot-chat.vim'
call plug#end()

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Foxe Chen

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2:58 PM (7 hours ago) 2:58 PM

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64-bitman left a comment (vim/vim#19580)

Can you check if setting bboth T_BSU and T_ESU to empty string only solves the issue, or does setting T_BSU or T_ESU to an empty (but leaving the other option as normal) also fix the issue?